Active matrix substrate and pixel defect correcting method therefor

ABSTRACT

An active matrix substrate facilitates correction of a pixel defect and a pixel defect correcting method. A laser target portion of a drain electrode extension portion is irradiated with laser light so as electrically disconnect a TFT from a subpixel electrode. Laser target portions are irradiated with laser light so as to melt an insulating layer, thereby establishing electrical connection between a drain electrode extension portion and a corrective connecting electrode and between a data signal line ( 13 ( m +1)) and the corrective connecting electrode. Laser target portions are irradiated with laser light, thereby establishing electrical connection between a drain electrode extension portion of a pixel P(n+1, m) and a corrective connecting electrode and between the data signal line ( 13 ( m +1)) and the corrective connecting electrode. Laser target portions are irradiated with laser light so as to separate part of the data signal line ( 13 ( m +1)) and use the separated part of the data signal line ( 13 ( m +1)) as a detour conductor.

This application is the U.S. national phase of International ApplicationNo. PCT/JP2006/302990 filed Feb. 21, 2006 which designated the U.S. andclaims priority to JP 2005-079394 filed Mar. 18, 2005, the entirecontents of each of which are hereby incorporated by reference.

TECHNICAL FIELD

The present invention relates to active matrix substrates that cancorrect a pixel defect, and to a pixel defect correcting method.

BACKGROUND ART

In the manufacturing process of active matrix substrates, foreignparticles, film residues, or the like, can cause a short circuit(source-drain leakage) between the source electrode and the drainelectrode of a TFT or a short circuit (source-gate leakage) between thesource electrode and the gate electrode thereof. Such leakage prevents anormal voltage (drain voltage) from being applied to the pixelelectrode, resulting in the appearance of a pixel defect in the form ofa white point or a black point, for example, on the display screen of aliquid crystal display device. This undesirably reduces themanufacturing yield of liquid crystal display devices.

To correct such a pixel defect, there have been proposed liquid crystaldisplay devices provided with a corrective connecting conductor betweenadjacent pixels (see, for example, Patent Documents 1 to 4). Accordingto these proposals, when a pixel defect occurs, a corrective connectingconductor is irradiated with laser light, for example, so that the pixelelectrode of the defective pixel is electrically connected to the pixelelectrode of the next pixel, whereby a voltage at the same potential asthe next pixel is applied to the pixel electrode of the defective pixel.In this way, the defective pixel is driven in an analogous manner to thenext pixel.

-   Patent Document 1: JP-A-S59-101693 (page 1)-   Patent Document 2: JP-A-H02-135320 (pages 1 and 4, FIG. 1)-   Patent Document 3: JP-A-H08-328035 (pages 1 and 5, FIG. 1)-   Patent Document 4: JP-A-2002-350901 (pages 17 and 24, FIG. 20)

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention

However, these proposed correcting methods require a correctiveconnecting conductor to be provided in such a way as to straddle theborder between the pixels. This undesirably reduces the aperture ratiowith an increase in the area of the corrective connecting conductor.

Additionally, in recent years, to reduce the dependence of γcharacteristics on a viewing angle, a method of dividing one pixel intotwo or more subpixels and applying different voltages to the resultantsubpixels has been increasingly adopted in liquid crystal displaydevices. With a conventional pixel defect correcting method, such aliquid crystal display device in which each pixel is provided with twoor more subpixels cannot achieve satisfactory image quality.

In view of the conventionally experienced problems described above, anobject of the present invention is to provide active matrix substratesand a pixel defect correcting method therefor that can easily andreliably correct a pixel defect without reducing the aperture ratio, thepixel defect caused by abnormalities such as source-drain leakage orsource-gate leakage in a TFT portion due to foreign particles, filmresidues, or the like, in the active matrix substrate in which eachpixel is provided with two or more subpixel electrodes, and that canimprove yields of liquid crystal display devices.

Another object of the present invention is to provide a pixel defectcorrecting method that can easily and reliably correct a pixel defectwithout reducing image quality, the pixel defect caused by abnormalitiesin a TFT portion in an active matrix substrate in which each pixel isprovided with two or more subpixel electrodes.

Means for Solving the Problem

Through an intensive study in search of a method for correcting a pixeldefect without reducing display quality, the pixel defect caused mainlyby abnormalities in a TFT portion in an active matrix substrate in whicheach pixel is provided with two or more subpixel electrodes, theinventors of the present invention have found out that, as compared withwhen all the subpixel electrodes of the defective pixel are corrected,when part of the subpixels of the defective pixel is corrected and theremainder thereof is left as a black point, the display quality isimproved. The reason is considered to be as follows. Certainly, bycorrecting a defect by applying a voltage to all the subpixel electrodesof the defective pixel from the TFT of a subpixel adjacent thereto, itis possible to prevent the pixel from appearing as a black or whitepoint. However, since the electrically connected subpixels are driven bythe same drain voltage, the corrected subpixels are lit with timingdifferent from their original lightning timing. Additionally, due to theimbalance in the capacitances of the subpixel electrodes, the drainvoltage whose value is different from its original set value is applied.This may result in an unsatisfactory display quality despite of defectcorrection.

The present invention is based on the above findings. According to oneaspect of the present invention, an active matrix substrate is providedwith: a plurality of scanning signal lines and data signal lines formedon the substrate; thin-film transistors provided at intersections of thesignal lines, the thin-film transistors each having a gate electrodeconnected to the scanning signal line and having a source electrodeconnected to the data signal line; and pixel electrodes each connectedto a drain electrode or a drain lead-out conductor of one of thethin-film transistors. Here, the pixel electrodes are each provided withtwo or more subpixel electrodes to which different voltages can beapplied. The data signal lines each have at least partially adouble-track structure. A corrective connecting electrode is formed in alayer including the scanning signal line. Part of the correctiveconnecting electrode overlaps the data signal line via an insulatinglayer, and another part thereof overlaps the drain electrode or thedrain lead-out conductor via the insulating layer.

Preferably, from a viewpoint of correcting a defective pixel withoutreducing the display quality, an identification mark for identifying asubpixel electrode of the two or more subpixel electrodes, the subpixelelectrode to which the highest effective voltage is applied, is formedin the scanning signal line or in the data signal line within an areasurrounded by lines of a double track of the data signal line.

Preferably, to identify a subpixel electrode to which the highesteffective voltage is applied while preventing an increase in theresistance of the scanning signal line or the data signal line, aprojection extending from the scanning signal line or the data signalline in the same plane is used as the identification mark.

According to another aspect of the present invention, a pixel defectcorrecting method corrects a pixel defect occurring in one of the activematrix substrates described above. Here, at least one subpixel electrodeof a defective pixel and a subpixel electrode of a pixel next to thedefective pixel are made to be at approximately the same potential byestablishing electrical connection therebetween via the data signal lineand the corrective connecting electrode, and the other subpixel of thedefective pixel is left as a black point. Incidentally, for a normallyblack liquid crystal display device that blocks illuminating light whenno voltage is applied to a pixel electrode, the subpixel is made toappear as a black point as follows. In a case of source-drain leakage, adrain lead-out conductor is cut so that no voltage is applied to thepixel electrode; in a case of source-gate leakage in the TFT portion, abranch of the gate or source of the TFT and the drain lead-out conductorare cut. On the other hand, for a normally white liquid crystal displaydevice that allows illuminating light to pass therethrough when novoltage is applied to the pixel electrode, in a case of source-drainleakage, a defective pixel is left as it is without performing anycorrection; in a case of source-gate leakage in the TFT portion, abranch of the gate or source of the TFT is cut.

Preferably, from a viewpoint of improving the display quality, at leastone subpixel electrode of a defective pixel and a subpixel electrode ofa pixel next to the defective pixel, the subpixel electrode to which thehighest effective voltage is applied, are made to be at approximatelythe same potential by establishing electrical connection therebetween.

By using the corrective connecting electrode, electrical connection isestablished as follows. A portion where the corrective connectingelectrode and the data signal line overlap each other and a portionwhere the corrective connecting electrode and the drain electrode or thedrain lead-out conductor overlap each other are melted by laserirradiation so as to establish electrical connection therebetween.Preferably, part of the data signal line electrically connected to thecorrective connecting electrode is separated from the remainder of thedata signal line.

ADVANTAGES OF THE INVENTION

According to the present invention, in an active matrix substrate, apixel electrode is provided with two or more subpixel electrodes towhich different voltages can be applied, a data signal line has at leastpartially a double-track structure, a corrective connecting electrode isformed in a layer including a scanning signal line, and part of thecorrective connecting electrode is made to overlap the data signal linevia an insulating layer, and the other part thereof is made to overlap adrain electrode or a drain lead-out conductor via the insulating layer.This makes it possible to easily and reliably correct a pixel defectcaused by abnormalities such as source-drain leakage or source-gateleakage in a TFT portion without reducing the aperture ratio, and toimprove yields of liquid crystal display devices.

According to the present invention, in a pixel defect correcting methodfor an active matrix substrate, part of subpixel electrodes of adefective pixel and a subpixel electrode of a pixel next to thedefective pixel are made to be at approximately the same potential byestablishing electrical connection therebetween via the data signal lineand the corrective connecting electrode, and the other subpixel of thedefective pixel is left as a black point. This helps improve the displayquality as compared with when all the subpixels of the defective pixelare corrected.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 A plan view showing an example of an active matrix substrateembodying the invention.

FIG. 2 A sectional view taken on the line A-A of FIG. 1.

FIG. 3 A sectional view taken on the line B-B of FIG. 1.

FIG. 4 A partially enlarged plan view showing another example of anidentification mark.

FIG. 5 A schematic diagram of an equivalent circuit of a liquid crystaldisplay device using the substrate shown in FIG. 1.

FIG. 6 An example of a waveform diagram showing voltages for driving theliquid crystal display device.

FIG. 7 A plan view showing an example of correction made to thesubstrate shown in FIG. 1.

FIG. 8 An outline diagram showing how to electrically connect acorrective connecting electrode to the drain electrode and to the datasignal line.

FIG. 9 A diagram showing the capacitance of a subpixel.

FIG. 10 A plan view showing another example of correction made to thesubstrate shown in FIG. 1.

FIG. 11 A plan view showing another example of the active matrixsubstrate embodying the invention.

FIG. 12 A plan view showing an example of correction made to thesubstrate shown in FIG. 11.

FIG. 13 A plan view showing another example of correction made to thesubstrate shown in FIG. 11.

LIST OF REFERENCE SYMBOLS

-   -   2 a, 2 a′, 2 b, 2 b′ Corrective connecting electrode    -   12 Scanning signal line    -   13 Data signal line    -   15 TFT (thin-film transistor)    -   21 a Insulating layer    -   121, 131 Projection (identification mark)

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, an active matrix substrate according to the presentinvention and a pixel defect correcting method using the same will bedescribed with reference to the accompanying drawings. However, thepresent invention is not limited to the embodiments specifically shownin these drawings. Unless otherwise noted, in this specification, aliquid crystal display device is assumed to be of a normally black type.

FIG. 1 is a plan view schematically showing the pixel structure of theactive matrix substrate embodying the invention, with respect to a pixelP(n, m) at row n and column m. FIGS. 2 and 3 are sectional views takenon the lines A-A and B-B, respectively, of FIG. 1. The pixel P(n, m)includes two subpixel electrodes 101 a and 101 b, which are arrangedcontiguously in the column direction. A scanning signal line 12(n) islaid between the pixels in the horizontal direction in this figure, anda data signal line 13(m) is laid between the pixels in the verticaldirection in this figure. Two auxiliary capacitance conductors 14O and14E are laid in such a way as to be parallel to the scanning signal line12(n), and are arranged above the subpixel electrode 101 a and below thesubpixel electrode 101 b, respectively. TFTs 15 a and 15 b serving as aswitching element are formed near the intersection of the scanningsignal line 12(n) and the data signal line 13(m).

A drain electrode extension portion 16 a of the TFT 15 a extends to theauxiliary capacitance conductor 14O, and overlaps it to form a portionfacing an auxiliary capacitance common electrode 141, which is anintegral part of the auxiliary capacitance conductor 14O, via aninsulating layer 21 a (shown in FIG. 2) and serving as an auxiliarycapacitance electrode 17 a. On this auxiliary capacitance electrode 17a, a contact hole 18 a is formed, whereby the drain electrode extensionportion 16 a and the subpixel electrode 101 a are connected to eachother (see FIG. 2). Likewise, a drain electrode extension portion 16 bextends to the auxiliary capacitance conductor 14E, and overlaps it toform a portion facing an auxiliary capacitance common electrode 142,which is an integral part of the auxiliary capacitance conductor 14E,via an insulating layer (not shown) and serving as an auxiliarycapacitance electrode 17 b. On this auxiliary capacitance electrode 17b, a contact hole 18 b is formed, whereby the drain electrode extensionportion 16 b and the subpixel electrode 101 b are connected to eachother.

Here, the data signal line 13 has a so-called “ladder” shapeddouble-track structure. As will be described later, at the time ofcorrection of a defective pixel, further improvement in the displayquality can be achieved if a subpixel electrode of the defective pixelis at the same potential as one of subpixel electrodes of the nextpixel, the one to which a higher effective voltage is applied. For thisreason, it is preferable to put an identification mark so that asubpixel electrode to which a higher effective voltage is applied can beidentified without actually applying a voltage. In this embodiment,since a higher effective voltage is applied to the subpixel electrode101 a, a projection (an identification mark) 131 is formed in a portionof the data signal line 13(m) located on one side of the subpixelelectrode 101 a.

Needless to say, since it is necessary simply to identify a subpixelelectrode to which the highest effective voltage is applied, aprojection may be instead formed on the side of the subpixel electrode101 b to which a lower effective voltage is applied. Alternatively, asshown in FIG. 4, a projection 121 may be formed in the scanning signalline 12. Instead, as an identification mark, any conventionally knownidentification mark such as a notch, a depression, or a printed mark maybe formed in the signal line. However, a notch or a depression formed inthe signal line as an identification mark may increase the resistance ofthe signal line, and thereby affect the display characteristics. On theother hand, a printed mark can disappear. It is for these reasons that aprojection is preferable as an identification mark when used incombination with a ladder-shaped data signal line.

As shown in FIGS. 1 and 3, a corrective connecting electrode 2 is formedin a layer containing the scanning signal line 12(n). One end of thecorrective connecting electrode 2 overlaps the drain electrode extensionportion 16 a via the insulating layer 21 a, and the other end thereofoverlaps a data signal line 13(m+1) via the insulating layer 21 a. Thereason that the corrective connecting electrode 2 and part of the drainelectrode extension portion 16 a are formed diagonally is that doing somakes them overlap a slit (not shown) formed in the subpixel electrodes101 a and 101 b or a common electrode (not shown) for aligning a liquidcrystal layer. This helps prevent a reduction in the aperture ratio ofthe liquid crystal display device.

As shown in FIG. 2, the auxiliary capacitance conductor 14O is formedbelow the contact hole 18 a with the insulating layer 21 a laid inbetween. This blocks light resulting from irregularities in thealignment of the liquid crystal layer, making it possible to improve theimage quality. Incidentally, the insulating layer 21 a forming anauxiliary capacitance is, for example, a gate insulating layer of a TFT.

FIG. 5 shows a schematic diagram of an equivalent circuit of the liquidcrystal display device shown in FIG. 1. In this figure, a liquid crystalcapacitance corresponding to a subpixel 101-a is represented by ClcO,and a liquid crystal capacitance corresponding to a subpixel 101-b isrepresented by ClcE. The liquid crystal capacitance ClcO of the subpixel101-a is formed with the subpixel electrode 101 a, the common electrode21, and the liquid crystal layer laid between them, and the liquidcrystal capacitance ClcE of the subpixel 101-b is formed with thesubpixel electrode 101 b, the common electrode 21, and the liquidcrystal layer laid between them. The subpixel electrodes 101 a and 101 bare connected to the data signal line 13(m) via the TFTs 15 a and 15 b,respectively, and the gate electrodes G of the TFTs are connected to acommon scanning signal line 12(n).

In FIG. 5, a first auxiliary capacitance formed for the subpixel 101-aand a second auxiliary capacitance formed for the subpixel 101-b arerepresented by CcsO and CcsE, respectively. The auxiliary capacitanceelectrode 17 a of the first auxiliary capacitance CcsO is connected tothe drain of the TFT 15 a via the drain electrode extension portion 16a, and the auxiliary capacitance electrode 17 b of the second auxiliarycapacitance CcsE is connected to the drain of the TFT 15 b via the drainelectrode extension portion 16 b. The points to which the auxiliarycapacitance electrodes 17 a and 17 b are connected are not limited tothose specifically shown in the figure, but may be otherwise as long asthe auxiliary capacitance electrodes 17 a and 17 b are electricallyconnected to the subpixel electrodes 101 a and 101 b, respectively, sothat they receive the same voltages applied to the subpixel electrodes101 a and 101 b. That is, the subpixel electrodes 101 a and 101 b simplyhave to be connected, directly or indirectly, to the auxiliarycapacitance electrodes 17 a and 17 b.

The auxiliary capacitance common electrode 141 of the first auxiliarycapacitance CcsO is connected to the auxiliary capacitance conductor14O, and the auxiliary capacitance common electrode 142 of the secondauxiliary capacitance CcsE is connected to the auxiliary capacitanceconductor 14E. With this configuration, it is possible to feed differentauxiliary capacitance common voltages to the auxiliary capacitancecommon electrodes 141 and 142 of the first auxiliary capacitance CcsOand the second auxiliary capacitance CcsE. As will be described later,the connection relationship between the auxiliary capacitance commonelectrodes 141 and 142 and the auxiliary capacitance conductors 14O and14E is appropriately selected depending on a driving method (such as dotinversion).

By feeding different auxiliary capacitance common voltages to the twoauxiliary capacitance conductors 14O and 14E in this configuration, itis possible to make the effective voltage of the subpixel electrode 101a higher than that of the subpixel electrode 101 b. This makes itpossible to make the brightness of the subpixel 101-a higher than thatof the subpixel 101-b. Different voltages can be applied to the subpixelelectrode 101 a and to the subpixel electrode 101 b based on thefollowing principle.

FIG. 6 shows voltage waveforms and timing of different signals inputtedto the pixel P(n, m) shown in FIG. 5. Character (a) represents awaveform of a display signal voltage (gray-scale signal voltage) Vs fedto the data signal line 13. Character (b) represents a waveform of ascanning signal voltage Vg fed to the scanning signal line 12, andcharacters (c) and (d) represent waveforms of auxiliary capacitancecommon voltages (VcsO, VcsE) fed to the auxiliary capacitance conductors14O and 14E, respectively. Characters (e) and (f) represent waveforms ofvoltages (VlcO, VlcE) applied to the liquid crystal capacitance ClcO ofthe subpixel 101-a and the liquid crystal capacitance ClcE of thesubpixel 101-b, respectively.

A driving method shown in FIG. 6 is an embodiment of the presentinvention applied to a liquid crystal display device adopting 1 H dotinversion and frame inversion.

The display signal voltage Vs applied to the data signal line 13 isinverted every time one scanning signal line is selected (at intervalsof a period of 1 H), and is opposite in polarity to the display signalvoltage applied to the next signal line (1 H dot inversion). Also, thedisplay signal voltages Vs applied to all the data signal lines 13 areinverted frame by frame (frame inversion).

In this example, the auxiliary capacitance common voltages VcsO and VcsEare inverted at intervals of a period of 2 H. The auxiliary capacitancecommon voltages VcsO and VcsE have waveforms with the same amplitude butshifted in phase by 180 degrees.

With reference to FIG. 6, the reason why the voltages (VlcO, VlcE)applied to the liquid crystal capacitance ClcO and to the liquid crystalcapacitance ClcE behave as shown in FIG. 6 will be described.

At time T₁, the scanning signal voltage Vg is shifted from a low level(VgL) to a high level (VgH), so that the TFTs 15 a and 15 b are broughtinto conduction, whereby the display signal voltage Vs fed to the datasignal line 13 is applied to the subpixel electrodes 101 a and 101 b.The voltage applied to both ends of the liquid crystal capacitances ClcOand ClcE equals a difference between the voltage at the subpixelelectrodes 101 a and 101 b and the voltage (Vcom) at the commonelectrode 21, namely VlcO=VlcE=Vs−Vcom.

At time T₂, when the scanning signal voltage Vg is shifted from a highvoltage VgH to a low voltage VgL (<Vs), the TFTs 15 a and 15 b aresimultaneously brought into out of conduction (an OFF state), wherebyall the subpixels and auxiliary capacitances are electricallydisconnected from the data signal line 13. At the same time, due to theinfluences of, for example, the parasitic capacitance in the TFTs 15 aand 15 b, a so-called pull-in effect occurs, reducing the voltages atthe subpixel electrodes 101 a and 101 b by ΔVd.

At time T₃, the voltage VlcO of the liquid crystal capacitance ClcOchanges under the influence of the voltage VcsO at the auxiliarycapacitance common electrode 141 of the auxiliary capacitance CcsOelectrically connected to the subpixel electrode 101 a forming theliquid crystal capacitance ClcO; the voltage VlcE of the liquid crystalcapacitance ClcE changes under the influence of the voltage VcsE at theauxiliary capacitance common electrode 142 of the auxiliary capacitanceCcsE electrically connected to the subpixel electrode 101 b forming theliquid crystal capacitance ClcE.

Here, suppose that, at time T₃, the auxiliary capacitance common voltageVcsO increases by VcsOp>0, and the auxiliary capacitance common voltageVcsE decreases by VcsEp>0. That is, let the total amplitude (Vp-p) ofthe auxiliary capacitance common voltage VcsO be VcsOp, and the totalamplitude of the auxiliary capacitance common voltage VcsE be VcsEp.

Let the total capacitance of the liquid crystal capacitance ClcO and theauxiliary capacitance CcsO be C_(pix)O, and the total capacitance of theliquid crystal capacitance ClcE and the auxiliary capacitance CcsE beC_(pix)E. Then,VlcO=Vs−ΔVd+VcsOp(CcsO/C _(pix) O)−Vcom,VlcE=Vs−ΔVd−VcsEp(CcsE/C _(pix) E)−Vcom.

Next, at time T₄, VlcO and VlcE are turned back to the voltage valuesobserved at time T₂ once again under the influence of the voltages VcsOand VcsE at the auxiliary capacitance common electrodes.VlcO=Vs−ΔVd−VcomVlcE=Vs−ΔVd−Vcom

This voltage change is repeated until Vg(n) becomes VgH in the nextframe. As a result, VlcO and VlcE are given different effective values.That is, let the effective value of VlcO be VlcO_(rms), and theeffective value of VlcE be VlcE_(rms). Then,VlcO _(rms) =Vs−ΔVd+(½)VcsOp(CcsO/C _(pix) O)−Vcom,VlcE _(rms) =Vs−ΔVd−(½)VcsEp(CcsE/C _(pix) E)−Vcom

-   -   (when (Vs−ΔVd−Vcom)>>VcsOp(CcsO/C_(pix)O)    -   and (Vs−ΔVd−Vcom)>>VcsEp(CcsE/C_(pix)E)).

Thus, let a difference between these effective values beΔVlc=VlcO_(rms)−VlcE_(rms). Then,ΔVlc={VcsOp(CcsO/C_(pix)O)+VcsEp(CcsE/C_(pix)E)}/2. As described above,by controlling the voltages applied to the auxiliary capacitance commonelectrodes 141 and 142 of the auxiliary capacitances CcsO and CcsErespectively connected to the subpixel electrodes 101 a and 101 b, it ispossible to apply different voltages to the subpixel electrode 101 a andthe subpixel electrode 101 b.

Alternatively, by giving VcsO a voltage value of VcsE and giving VcsE avoltage value of VcsO, it is possible to make smaller the effectivevalue of VlcO and make greater the effective value of VlcE. Instead, byconnecting the auxiliary capacitance conductor 14O to the auxiliarycapacitance common electrode 142 of the auxiliary capacitance CcsE andconnecting the auxiliary capacitance conductor 14E to the auxiliarycapacitance common electrode 141 of the auxiliary capacitance CcsO, itis also possible to make smaller the effective value of VlcO and makegreater the effective value of VlcE.

Here, since frame inversion driving is performed, the polarity of Vs isinverted in the next frame, and Vlc<0. In this case, by inverting thepolarities of VcsO and VcsE in synchronism therewith, it is possible toachieve the same effects as in the case described above.

In the active matrix substrate configured as described above, if a pixeldefect occurs as a result of source-drain leakage, source-gate leakage,or the like, due to foreign particles or film residues, for example, inthe TFT portion of the pixel P, and is left uncorrected, the pixel Pappears as a white point. This causes the substrate to be rejected as adefective. To avoid this, correction is made by applying a drain voltageto part of the subpixels of the pixel P from the next pixel.

FIG. 7 shows an example of a correcting method. The correcting methodshown in FIG. 7 is adopted when a pixel defect occurs due tosource-drain leakage in the TFT portion of the pixel P(n, m). In thisexample, a subpixel electrode (a “bright” electrode) 102 a of a pixelP(n+1, m) arranged below the defective pixel P(n, m) and the subpixel101 b of the defective pixel P(n, m) are made to be at approximately thesame potential by means of the corrective connecting electrodes 2 a′ and2 b, and the other subpixel of the defective pixel P(n, m), namely thesubpixel 101-a is left as a black point. A specific correcting method isas follows.

A laser target portion 71 of the drain electrode extension portion 16 bis irradiated with laser light from the front or back of the substrateso as to electrically disconnect the TFT 15 b affected by abnormalitiesfrom the subpixel electrode 101 b. Then, as shown in FIG. 8, lasertarget portions 72 and 73 are irradiated with laser light so as to meltthe insulating layer 21 a, thereby establishing electrical connectionbetween the drain electrode extension portion 16 b and the correctiveconnecting electrode 2 b and between the data signal line 13(m+1) andthe corrective connecting electrode 2 b. Likewise, laser target portions74 and 75 are irradiated with laser light, thereby establishingelectrical connection between the drain electrode extension portion 16a′ of the pixel P(n+1, m) and the corrective connecting electrode 2 a′and between the data signal line 13(m+1) and the corrective connectingelectrode 2 a′. Then, laser target portions 76 to 79 are irradiated withlaser light so as to separate part of the data signal line 13(m+1) anduse the separated part of the data signal line 13(m+1) as a detourconductor.

On the other hand, a laser target portion 70 of the drain electrodeextension portion 16 a is irradiated with laser light so as toelectrically disconnect the TFT 15 b from the subpixel electrode 101 a,whereby the subpixel 101-a is left as a black point.

In the correcting method here, any conventionally known laser can beused, examples including a YAG laser (wavelength: 266 nm and 532 nm).Different types of lasers may be used appropriately in accordance withthe intended use, such as cutting an electrode or melting an insulatinglayer.

As described above, by forming a detour shown in FIG. 7 (indicated byarrows in the figure), the drain voltage applied to the subpixelelectrode 102 a of the pixel P(n+1, m) is applied also to the subpixelelectrode 101 b of the defective pixel P(n, m). As a result, thesubpixel 101-b is made to perform the same display operation as thesubpixel 102-a, and is given substantially the same brightness as thesubpixel 102-a. This helps improve the display quality. As will bedescribed below, it has been theoretically proved that the brightness ofthe subpixel 101-b is substantially the same as that of the subpixel102-a.

With reference to FIG. 9, the total capacitance C_(pix) of a subpixelbefore correction is given byC _(pix) =C _(LC) +C _(Cs) +C _(sd) +C _(gd)where C_(sd)=C_(sd1)+C_(sd2),

C_(sd1) being the capacitance of a data signal line of a pixel to whichit belongs, the data signal line laid within a subpixel electroderegion, and

C_(sd2) being the capacitance of a data signal line of the other pixel,the data signal line laid within the subpixel electrode region.

After correction is performed, since the area of the subpixel isdoubled, and the subpixel is driven by one TFT, the total capacitanceC′_(pix) is given byC′ _(pix)=2C _(LC)+2C _(Cs)+2C _(sd) +C _(gd).In general, C_(gd) is a few percent of C_(pix). Therefore, C′_(pix) canbe regarded as twice as large as C_(pix).

Here, the pull-in voltage ΔV_(d) at the drain before correction is givenbyΔV _(d)=(C _(gd) /C _(pix))×V _(gpp)

where V_(gpp) is the amplitude of the gate voltage. On the other hand,the pull-in voltage ΔV_(d)′ after correction is given byΔV_(d)′=(C_(gd)/C′_(pix))×V_(gpp). Thus, the pull-in voltage ΔV_(d)′after correction is a half of the voltage ΔV_(d) before correction.

The amount of change ΔV_(cs) in the drain voltage caused by theauxiliary capacitance voltage V_(cs) before correction is given byΔV _(cs)=(C _(cs) /C _(pix))×V _(cspp)where V_(cspp) is the amplitude of the auxiliary capacitance voltage. Onthe other hand, since C_(cs) after correction is twice as large as thatbefore correction, the amount of voltage change ΔV′_(cs) aftercorrection is given by ΔV_(cs)=(2 C_(cs)/C′_(pix))×V_(cspp). Thus, theamount of voltage change ΔV′_(cs) after correction is substantially thesame as that before correction.

As described above, the only change in the drain voltage caused by pixelcorrection is that the pull-in voltage ΔV_(d) is reduced in half. Thus,even after correction, the brightness of the pixel is substantially thesame.

FIG. 10 shows another example of a pixel correcting method. As is thecase with the correcting method described above, the correcting methodshown in FIG. 10 is adopted when a pixel defect occurs due tosource-drain leakage in the TFT portion of the pixel P(n, m); it differsfrom the correcting method described above in that a subpixel electrode(a “dark” electrode) 100 b of a pixel P(n−1, m) arranged above thedefective pixel P(n, m) and the subpixel 101 a of the defective pixelP(n, m) are made to be at approximately the same potential by means ofthe corrective connecting electrodes 2 b′ and 2 a.

The specific correction procedure is the same as that described above,and therefore only an outline thereof will be described. A laser targetportion 81 of the drain electrode extension portion 16 a is irradiatedwith laser light so as to electrically disconnect the TFT 15 a affectedby abnormalities from the subpixel electrode 101 a. Then, laser targetportions 82 and 83 are irradiated with laser light, thereby establishingelectrical connection between the drain electrode extension portion 16 aand the corrective connecting electrode 2 a and between the data signalline 13(m+1) and the corrective connecting electrode 2 a. Likewise,laser target portions 84 and 85 are irradiated with laser light, therebyestablishing electrical connection between the drain electrode extensionportion 16 b′ of the pixel P(n−1, m) and the corrective connectingelectrode 2 b′ and between the data signal line 13(m+1) and thecorrective connecting electrode 2 b′. Furthermore, laser target portions86 to 89 are irradiated with laser light so as to separate part of thedata signal line 13(m+1) and use the separated part of the data signalline 13(m+1) as a detour conductor.

As described above, by forming a detour shown in FIG. 10 (indicated byarrows in the figure), the drain voltage applied to the subpixelelectrode 100 b of the pixel P(n−1, m) is applied also to the subpixelelectrode 101 a of the defective pixel P(n, m). As a result, thesubpixel 101-a is made to perform the same display operation as thesubpixel 100-b, and is given substantially the same brightness as thesubpixel 100-b. This helps improve the display quality.

Incidentally, as compared with when the drain voltage at a lowereffective voltage side of the next pixel is applied to the subpixelelectrode of the defective pixel (a correcting method shown in FIG. 10),when the drain voltage at a higher effective voltage side of the nextpixel is applied thereto (a correcting method shown in FIG. 7), betterdisplay quality is obtained. That is, as compared with when thecorrected defective pixel is composed of a “dark” subpixel and a blackpoint, when it is composed of a “bright” subpixel and a black point,better display quality is obtained. After the assembly of the liquidcrystal panel, a subpixel electrode to which the highest effectivevoltage is applied can be identified by illuminating the liquid crystalpanel. However, it is impossible to illuminate the liquid crystal panelin the manufacturing process of the substrate. For this reason, asdescribed above, it is necessary to form a projection (an identificationmark) 131 in the substrate for easy identification of a subpixelelectrode to which the highest effective voltage is applied.

Next, a defect correcting method adopted in a case where the number ofsubpixels is three will be described. FIG. 11 is a plan viewschematically showing the pixel structure of an active matrix substrate.A pixel P(n−1, m) and a pixel P(n, m) are next to each other in thecolumn direction, and include subpixel electrodes 100 a to 100 c andsubpixel electrodes 101 a to 101 c, respectively, arranged contiguouslyin the column direction. Scanning signal lines 12(n−1) and 12(n) areformed between the pixels in the horizontal direction in this figure,and data signal lines 13(m) and 13(m+1) are formed between the pixels inthe vertical direction in this figure. Auxiliary capacitance conductors14O and 14E are formed between the subpixel electrodes so as to beparallel to the scanning signal lines 12. A TFT 15 serving as aswitching element is formed near the intersection of the scanning signalline 12 and the data signal line 13, and each pixel is provided withthree TFTs 15.

In the pixel P(n, m), a drain electrode extension portion 16 a extendsfrom the TFT 15 to the auxiliary capacitance conductor 14E, and overlapsit to form a portion facing an auxiliary capacitance common electrode142, which is an integral part of the auxiliary capacitance conductor14E, via an insulating layer (not shown) and serving as an auxiliarycapacitance electrode 17 a. On this auxiliary capacitance electrode 17a, a contact hole 18 a is formed, whereby the drain electrode extensionportion 16 a and the subpixel electrode 101 a are connected to eachother. Likewise, a drain electrode extension portion 16 c crosses theauxiliary capacitance conductor 14E and reaches the auxiliarycapacitance conductor 14O, and overlaps it to form a portion facing anauxiliary capacitance common electrode 141, which is an integral part ofthe auxiliary capacitance conductor 14O, via an insulating layer (notshown) and serving as an auxiliary capacitance electrode 17 c. On thisauxiliary capacitance electrode 17 c, a contact hole 18 c is formed,whereby the drain electrode extension portion 16 c and the subpixelelectrode 101 c are connected to each other. On the other hand, a drainelectrode extension portion 16 b extends from the TFT 15, then comesinto contact with the drain electrode extension portion 16 c, and isthen connected to the subpixel electrode 101 b through a contact hole 18b.

A corrective connecting electrode 2 c is formed in a layer including thescanning signal line 12(n). The corrective connecting electrode 2 coverlaps the drain electrode extension portions 16 a to 16 c via theinsulating layer, and overlaps the data signal line 13(m+1) via theinsulating layer.

On the other hand, in the pixel P(n−1, m), a drain electrode extensionportion 16 a′ extending from the TFT 15′ crosses the auxiliarycapacitance conductor 14E′ and reaches the auxiliary capacitanceconductor 14O′, and overlaps it to form a portion facing an auxiliarycapacitance common electrode 141′, which is an integral part of theauxiliary capacitance conductor 14O′, via an insulating layer (notshown) and serving as an auxiliary capacitance electrode 17 a′. On thisauxiliary capacitance electrode 17 a′, a contact hole 18 a′ is formed,whereby the drain electrode extension portion 16 a′ and the subpixelelectrode 100 a are connected to each other. Drain electrode extensionportions 16 b′ and 16 c′ are connected together on their way to theauxiliary capacitance conductor 14E′, and overlap it to form a portionfacing an auxiliary capacitance common electrode 142′, which is anintegral part of the auxiliary capacitance conductor 14E′, via aninsulating layer (not shown) and serving as an auxiliary capacitanceelectrode 17 b′. On this auxiliary capacitance electrode 17 b′, acontact hole 18 b′ is formed, whereby the drain electrode extensionportions 16 b′ and 16 c′ and the subpixel electrode 100 b are connectedto each other. Furthermore, a drain electrode extension portion 16 dextends from the auxiliary capacitance electrode 17 b′, crosses theauxiliary capacitance conductor 14O′, and reaches the subpixel electrode100 c, where it is connected to the subpixel electrode 100 c through acontact hole 18 c′.

Voltage control of the subpixel electrodes will be described, taking upthe pixel P(n, m) as an example. The same effective voltage is appliedto the subpixel electrodes 101 b and 101 c. In addition, as describedabove, different auxiliary capacitance common voltages are fed to thetwo auxiliary capacitance conductors 14O and 14E. This makes theeffective voltage of the subpixel electrode 101 a higher than those ofthe subpixel electrodes 101 b and 101 c, and makes the brightness of thesubpixel 101-a higher than those of the subpixels 101-b and 101-c. Thismakes it possible to eliminate unnaturalness in a rectilinear patternimage when it is displayed, and to reduce the dependence of γcharacteristics on a viewing angle.

In the active matrix substrate configured as described above, if a pixeldefect occurs as a result of source-drain leakage due to foreignparticles, film residues, or the like, in the TFT 15 of the pixel P(n,m), the pixel defect is corrected by applying a drain voltage from thenext pixel P(n−1, m) to part of the subpixels of the pixel P(n, m).

FIG. 12 shows an example of a correcting method. The exemplarycorrecting method shown in FIG. 12 is performed in such a way that adrain voltage is applied from the subpixel electrode (a “bright”electrode) 100 a of the pixel P(n−1, m) arranged above the defectivepixel P(n, m) to the subpixel electrodes 101 a and 101 c of thedefective pixel P(n, m) to drive the subpixels, and the other subpixel101-b of the defective pixel P(n, m) is left as a black point.Specifically, correction is performed as follows.

Laser target portions 5 a to 5 c of the drain electrode extensionportions 16 a to 16 c are irradiated with laser light so as to cut theelectrode, thereby electrically disconnecting the TFT 15 affected byabnormalities from the subpixel electrodes 101 a to 101 c. Likewise, alaser target portion 5 d laid between a portion where the drainelectrode extension portions 16 b and 16 c are connected together andthe contact hole 18 b is irradiated with laser light so as to cut theelectrode, thereby de-energizing the drain electrode extension portions16 b and 16 c. Then, laser target portions 5 e to 5 g are irradiatedwith laser light so as to melt the insulating layer (not shown), therebyestablishing electrical connection between the drain electrode extensionportions 16 a and 16 c and the corrective connecting electrode 2 c andbetween the data signal line 13(m+1) and the corrective connectingelectrode 2 c (see FIG. 8).

Laser target portions 5 h and 5 i are irradiated with laser light,thereby establishing electrical connection between the drain electrodeextension portion 16 a′ of the pixel P(n−1, m) and the correctiveconnecting electrode 2 d and between the data signal line 13(m+1) andthe corrective connecting electrode 2 d. Then, laser target portions 5 jto 5 l are irradiated with laser light so as to separate part of thedata signal line 13(m+1) and use the separated part of the data signalline 13(m+1) as a detour conductor. Also in this example, aforementionedexamples of laser can be used.

As described above, by forming a detour shown in FIG. 12 (indicated byarrows in the figure), the drain voltage applied to the subpixelelectrode 101 a of the pixel P(n−1, m) is applied also to the subpixelelectrodes 101 a and 101 c of the defective pixel P(n, m). As a result,the subpixels 101-a and 101-c are made to perform the same displayoperation as the subpixel 100-a, and is given substantially the samebrightness as the subpixel 100-a. This helps greatly improve the displayquality.

FIG. 13 shows another example of a pixel correcting method. As is thecase with the correcting method shown in FIG. 12, the correcting methodshown in FIG. 13 is adopted when a pixel defect occurs due tosource-drain leakage in the TFT portion of the pixel P(n, m); it differsfrom the correcting method shown in FIG. 12 in that the drain voltage isapplied from the subpixel electrodes (“dark” electrodes) 100 b and 100 cof the pixel P(n−1, m) to the subpixels 101 a and 101 c of the defectivepixel P(n, m).

The specific correction procedure is the same as that described above,and therefore only an outline thereof will be described. Laser targetportions 6 a to 6 c of the drain electrode extension portions 16 a to 16c of the pixel P(n, m) are irradiated with laser light so as to cut theelectrode, thereby electrically disconnecting the TFT 15 affected byabnormalities from the subpixel electrodes 101 a to 101 c. Likewise, alaser target portion 6 d laid between a portion where the drainelectrode extension portions 16 b and 16 c are connected together andthe contact hole 18 b is irradiated with laser light so as to cut theelectrode, thereby de-energizing the drain electrode extension portions16 b and 16 c. Then, laser target portions 6 e to 6 g are irradiatedwith laser light so as to melt the insulating layer (not shown), therebyestablishing electrical connection between the drain electrode extensionportions 16 a and 16 c and the corrective connecting electrode 2 c andbetween the data signal line 13(m+1) and the corrective connectingelectrode 2 c (see FIG. 8).

Laser target portions 6 h and 6 i are irradiated with laser light,thereby establishing electrical connection between the drain electrodeextension portion 16 d of the pixel P(n−1, m) and the correctiveconnecting electrode 2 d and between the data signal line 13(m+1) andthe corrective connecting electrode 2 d. Then, laser target portions 6 jto 6 l are irradiated with laser light so as to separate part of thedata signal line 13(m+1) and use the separated part of the data signalline 13(m+1) as a detour conductor.

As described above, by forming a detour shown in FIG. 13 (indicated byarrows in the figure), the drain voltage applied to the subpixelelectrodes 100 b and 100 c of the pixel P(n−1, m) is applied also to thesubpixel electrodes 101 a and 101 c of the defective pixel P(n, m). As aresult, the subpixels 101-a and 101-c are made to perform the samedisplay operation as the subpixels 100-b and 100-c, and are givensubstantially the same brightness as the subpixels 100-b and 100-c. Thishelps improve the display quality. As is the case where the number ofsubpixels is two, in a case where the number of subpixels is three, ascompared with when the drain voltage at a lower effective voltage sideof the next pixel is applied to the subpixel electrode of the defectivepixel, when the drain voltage at a higher effective voltage side of thenext pixel is applied thereto, better display quality is obtained. Asdescribed above, it is preferable to form a projection (anidentification mark) 131 in the substrate for easy identification of asubpixel electrode to which the highest effective voltage is applied.

INDUSTRIAL APPLICABILITY

With an active matrix substrate of the present invention, it is possibleto easily and reliably correct a pixel defect caused by abnormalitiessuch as source-drain leakage or source-gate leakage in a TFT portionwithout reducing the aperture ratio, and to improve yields of liquidcrystal display devices. Furthermore, with a correcting method for anactive matrix substrate of the present invention, as compared with whenall the subpixels of the defective pixel are corrected, it is possibleto improve the display quality.

1. An active matrix substrate comprising: a plurality of scanning signallines and data signal lines formed on the substrate; thin-filmtransistors provided at intersections of the signal lines, the thin-filmtransistors each comprising a gate electrode connected to the scanningsignal line and comprising a source electrode connected to the datasignal line; and pixel electrodes each connected to a drain electrode ora drain lead-out conductor of one of the thin-film transistors, whereinthe pixel electrodes, each comprise two or more subpixel electrodes towhich different voltages can be applied, wherein the data signal lineseach comprise at least partially a double-track structure, wherein acorrective connecting electrode is formed in a layer including thescanning signal line, wherein part of the corrective connectingelectrode overlaps the data signal line via an insulating layer, andanother part thereof overlaps the drain electrode or the drain lead-outconductor via an insulating layer.
 2. The active matrix substrate ofclaim 1, wherein an identification mark for identifying a subpixelelectrode of the two or more subpixel electrodes, the subpixel electrodeto which a highest effective voltage is applied, is formed in thescanning signal line or in the data signal line within an areasurrounded by lines of a double track of the data signal line.
 3. Theactive matrix substrate of claim 2, wherein the identification mark is aprojection extending from the scanning signal line or the data signalline in a same plane.
 4. A pixel defect correcting method for correctinga pixel defect occurring in an active matrix substrate, the activematrix substrate comprising; a plurality of scanning signal lines anddata signal lines formed on the substrate; thin-film transistorsprovided at intersections of the signal lines, the thin-film transistorseach comprising a gate electrode connected to the scanning signal lineand comprising a source electrode connected to the data signal line;pixel electrodes each connected to a drain electrode or a drain lead-outconductor of one of the thin-film transistors, the pixel electrodes eachcomprise two or more subpixel electrodes to which different voltages canbe applied; wherein the data signal lines each comprise at leastpartially a double-track structure; wherein a corrective connectingelectrode is formed in a layer including the scaning signal line;wherein part of the corrective connecting electrode overlaps the datasignal line via an insulating layer, and another part thereof overlapsthe drain electrode or the drain lead-out conductor via an insulatinglayer; the method comprising; making at least one subpixel electrode ofa defective pixel and a subpixel electrode of a pixel next to thedefective pixel, to be at approximately a same potential by establishingelectrical connection therebetween via the data signal line and thecorrective connecting electrode, and another subpixel of the defectivepixel is left as a black point.
 5. A pixel defect correcting methodaccording to claim 4, wherein at least one subpixel electrode of adefective pixel and a subpixel electrode of a pixel next to thedefective pixel are made to be at approximately a same potential byestablishing electrical connection therebetween, the subpixel next tothe defective pixel being the subpixel electrode to which a highesteffective voltage is applied.
 6. A pixel defect correcting method,according to claim 4, wherein a portion where the corrective connectingelectrode and the data signal line overlap each other and a portionwhere the corrective connecting electrode and the drain electrode or thedrain lead-out conductor overlap each other are melted by laserirradiation so as to establish electrical connection therebetween.
 7. Apixel defect correcting method according to claim 4, further comprising:separating part of the data signal line electrically connected to thecorrective connecting electrode from a remainder of the data signalline.